1. Field of the Invention
The present invention relates to a method and apparatus for processing a conductive thin film formed on the surface of an insulating substrate, more particularly relates to a method and apparatus for processing a molybdenum or other metal thin film used as the bottom electrode of a thin film solar cell or an indium tin or other transparent conductive thin film used as a top electrode. The transparent conductive thin film of the present invention can be utilized as an electrode of a light-receiving surface of a solar cell and also a transparent electrode of a liquid crystal display panel, plasma display panel, organic electroluminescence device, or other various types of display devices or as a heat generating element of a defroster.
2. Description of the Related Art
Thin film solar cells include a typical types ones having a basic structure of a back surface glass substrate/molybdenum thin film or other bottom electrode/CIS (Cu—In—S, Cu—In—Se) or other semiconductor thin film/ITO (indium tin oxide) or other transparent conductive oxide (TCO) thin film top electrode and ones having a basic structure of a light incident side glass substrate/ITO (indium tin oxide) or other transparent conductive oxide (TCO) thin film top electrode/amorphous silicon semiconductor thin film/metal bottom electrode. In each type, generally a structure comprised of a large number of unit cells arranged planarly in parallel on a glass substrate and having adjoining cells connected in series has been employed.
To fabricate this array, a processing step of patterning the molybdenum thin film (bottom electrode) or TCO thin film (top electrode) formed as a continuous film on a glass substrate to divide it corresponding to the unit cells is necessary. Similar patterning of unit cells is also performed on the semiconductor thin films formed on these electrode thin films etc. There has therefore been room for improvement in the patterning of these electrode thin films.
As the conventional methods of patterning a transparent conductive film, the laser patterning method and the etching method have been the most general. The laser patterning method, as shown in Fig. 11, focuses a high output laser beam on a transparent conductive film 12 to locally heat it and thereby vaporize or peel off and remove the transparent conductive film 12 at the parts irradiated by the laser to obtain the desired shape. Note that in Fig. 11, reference numeral 10 indicates a substrate, 12 indicates a transparent conductive film, 61 indicates a high output laser oscillator, 62 indicates an attenuator, 63 indicates a controller, 64 indicates a mirror, 65 indicates a beam forming optical system, and 66 indicates a condensing lens.
The laser patterning method enables high speed patterning with a smaller number of steps, so is being used for patterning solar cells and other objects requiring processing over a large area at a high speed. However, there have been the problems that when the conditions for focusing the laser beam are not suitable, the glass or plastic substrate 10 ends up being damaged, the laser oscillator 61 is expensive, tremendous labor is required for maintenance and management for maintaining the performance of the equipment, etc.
The etching method, as shown in Figs. 12A to 12E, coats a transparent conductive film 12 on a substrate 10 (Fig. 12A) with a photoresist 71 (Fig. 12B), patterns this photoresist film 71 to form the targeted mask 72 on the transparent conductive film 12 (Fig. 12C), removes only the parts exposed from the mask 72 of the transparent conductive film 12 by wet etching or dry etching (Fig. 12D), then removes the resist 71 (72) (Fig. 12E) to obtain a transparent conductive film 12 having the targeted shapes of pattern grooves 12a. 
In this etching method, a step for processing the mask other than processing the transparent conductive film 12 itself and a step for removing the mask are necessary. The overall number of steps increase, so there was the problem that the product costs rose.
The prior known publications disclose the following. Japanese Patent Publication (A) No. 2001-210851 discloses patterning a molybdenum, ITO, or other electrode thin film by a laser beam. According to this, as explained above, there were the problems that a laser oscillator is expensive and tremendous labor is required for maintenance and management for maintaining the performance of the equipment.
The inventors tried to solve the problem of patterning by a laser beam by the so-called “lift-off method” of forming patterns on a substrate in advance by a photoresist, depositing an electrode thin film from above, then peeling off the photoresist patterns and the parts of the electrode thin film on them, but found the problem that the increase in the number of steps led to an increase in the production costs.
Further, Japanese Patent Publication (A) No. 2001-119048 discloses to use the mechanical scribe method to pattern an electrode thin film. The inventors tried this, but found the problem that since the molybdenum thin film forming the electrode thin film is high in hardness, patterning is difficult.
As other known publications, Japanese Patent Publication (A) No. 2000-114555 discloses to use ZnO as a transparent conductive film, pattern this by laser scribing, then chemically etch this. Further, Japanese Patent Publication (A) No. 7-130701 discloses to pattern a transparent conductive film by wet etching using as a mask a resist pattern with edges tapered by adjusting the amount of exposure and amount of development at the time of photolithography or using different masks for a plurality of etchings to form step shapes and thereby form a gentle slant at the pattern edges.